There is considerable controversy about what the comparative roles of estrogen and testosterone in determining bone turnover in aging men. Patients will be temporarily and transgenely made hypogonad by administration of Lupron. They will be covered by testosterone patches until the study period begins to prevent symptoms. The patches will be withdrawn and they will be treated with either placebo plus letrozole (to prevent aromatizatin of androgens to estrogens), testosterone plus letrozole, estrogen or estrogen plus testosterone. The effects on bone turnover will be determined by assessment of biochemical markers.